The development of a wind tunnel with continuous control over the air flow parameters has been increasingly demanded as it helps in measuring aerodynamic forces, pressure distribution, or other aerodynamic-related characteristics. Since the air speed in a wind tunnel is determined completely by the geometry of the nozzle, it is necessary to provide a different nozzle shape for each different required speed. To change the effective cross-sectional area of the entrance end of the tunnel the nozzle must be changed, an operation which usually requires several hours. This not only adds considerably labor cost of the testing operation, but also, in elect, wastes valuable time in which the test equipment is idle. Further, this type of wind tunnel precludes changing the effective cross-sectional area of the tunnel while it is in operation, but also does not allow a smooth change in such area, since the different replacement nozzles must of necessity differ appreciably from each other.
Therefore, there is need for a variable nozzle for a wind tunnel device that allows for valid and effective aerospace testing at differing pressures, air flow rates and temperatures, even at subsonic speeds.